Glycerol release from adipose tissue is being studied in obese subjects on various diets before and after weight reduction. Intravenous infusion of glycerol either continuously or by a single injection are used to provide changes in plasma glycerol levels which are then used for calculation of turnover rate. This rate is compared directly to the rate of glycerol release from adipose tissue in-vitro. A variety of other phenomena are under observation in obese subjects, undergoing weight reduction by caloric restriction. These include changes in plasma amino acid, thyroid hormones and pituitary responsivity to releaser hormones or provocative tests for hormone release. An immunoassay for cholecystokinin is being developed for use in this subject population.